1. Field of the Invention
The present invention relates to an amplifier including a first transistor whose emitter is connected to an amplifier output and whose collector is connected to a first of two current supply terminals, with a base of the first transistor being connected to an input.
A primary object of the invention is to provide an amplifier, particularly an audiofrequency amplifier which will reproduce true-to-life sound (speech, music, etc.).
2. Description of the Related Art
Audiofrequency amplifiers are well known in semiconductor constructions, where great efforts have been made to provide lifelike sound reproduction. In practice, however, developments have not proceeded to any great extent, since tube amplifiers are still considered to provide splendid sound in comparison with semiconductor constructions.
Accordingly, an object of the present invention is to provide a semiconductor amplifier which while affording the advantages associated with a class-A amplifier will not have the dominant drawback of the class-A amplifier, namely poor efficiency.
For instance, true-to-life sound reproduction can be achieved with a tube-equipped class-A amplifier that includes a constant current generator (or a resistor), by virtue of the fact that current amplification can be achieved in a small delimited area of the working curve of the current amplifying unit. This results in good linearity while eliminating any overtone distortions.
The inventive amplifier stage includes a first transistor whose emitter is connected to an amplifier output and whose collector is connected to a first of two current supply terminals, the base of the first transistor being connected to a signal input.
The invention is directed to an amplifier including a first transistor whose emitter is connected to an amplifier output and whose collector is connected to a first of two current supply terminals, with a base of the first transistor being connected to an input. Thus, in order to achieve very pure sound of high transparency with such an amplifier at the same time as the efficiency of the amplifier is much greater than the efficiency of a class-A amplifier, the inventive amplifier is designed so as to include a sensing circuit (constant load circuit) between the emitter of the first transistor and the second current supply terminal, and the sensing circuit is adapted to ensure that the current through the first transistor will always exceed a lowest value, so that the transistor will constantly lie in a delimited, generally linear area of its working curve.
In one embodiment of the invention, the emitter of the first transistor may be connected to the amplifier output via a first conductor part which includes a first resistance, wherewith a second conductor part is connected to the first conductor part in parallel and contains a second resistance and a diode in series therewith.
The constant load circuit includes a second transistor whose collector is connected to the second current supply terminal and whose emitter is connected to the load. The constant load circuit also includes a shunt line between the second current supply terminal and the emitter of the first transistor, wherewith the shunt line of the constant load circuit includes an adjustable zener diode or a corresponding device which is set so that the diode of the second conductor part will not conduct when the amplifier idles. The input of the second transistor is connected to the shunt line between the second current supply terminal and the adjustable diode. A third transistor may be connected in the Darlington-arrangement with the second transistor in the constant load circuit. The constant load circuit is adapted to-ensure that current will continue to flow through the first resistance (resistor) of the first conductor part. A fourth transistor is suitably connected in a Darlington-arrangement with the first transistor, between said input and the first transistor. The constant load circuit is adapted to ensure that the first and the fourth transistor will continue to conduct even on the negative half of the output signal.